Armpit Blood clots

For the past year or so, I have been getting on and off blood clots in the armpit area. Upon consulting my doc, he told me to take some antibiotic and that itwould go away---this has not been the case. On and off, about once in a month or two months, one of my two arms get affected. A clot forms and then sooner or later it pops and bleeds for a while and goes away. Usually, I could tell when it is coming, I begin to feel a lump in the arm pit area. Please advise as to what I should do. Thanks.